1. Field of the Invention
The present invention relates to a catheter with a balloon for expanding a constricted valve, of the heart, or a constricted or occluded blood vessel and thereby normalizing blood flow in a medical treatment.
2. Background of the Invention
As material for the balloon for use with a catheter, thin membranes (films) of synthetic resins, such as polyethylene, polyvinyl chloride or polyester, which have no stretchability but have pressure resistance, have been used for preventing damage to blood vessels caused by an excessive expansion. It is preferable that these balloons are not expanded, because, if they expand, the surfaces thereof become slippery and cause the balloons to slip out of place, and when they are deflated, wrinkles are produced thereon which rub the inner walls of blood vessels, cause damages and accelerate formation of thrombi.
Therefore, it has been proposed, in order to improve the balloon and prevent the formation of wrinkles when deflation occurs, to use a polyurethane or a silicone as a material for the balloon (Japanese Laid-Open Patent No. 91970/1984 and No. 103,453/1986) or shrink the balloon (Japanese Laid-Open Patent No. 125,386/1978), or prevent excessive expansion or make the expansion uniform by incorporating a knitted fabric in the balloon.
In addition, it has been proposed to use rubber as a balloon material and form a guitar-shaped constricted part on the balloon by pinching the balloon with a knitted fabric having several stripes of bands for pinching a constricted valve of the heart so that the balloon does not slip out (Japanese Patent No. 23506/1982).
However, when these balloons are used, the outer diameters become large, and exposure and incision of a blood vessel is required where the balloon is to be inserted. This results in a longer time for recovery and inconvenience after medical treatment.
On the other hand, it is proposed in Japanese Laid-Open Patent No. 103,453/1986 that a knitted fabric be put in a balloon. This requires a complicated operation consisting of knitting a parallel-twisted yarn of a polyamide yarn and a urethane yarn as a covering on the outer surface of a balloon expanded to a required expanded diameter. In addition, the diameter of the balloon cannot be made small and the balloon cannot be stretched in the longitudinal direction.